The objective of this research is to continue to investigate immunity and other mechanisms of resistance to infection with Hemophilus influenzae type b (HIB). The role of serum bactericidal activity in protection against HIB disease will be investigated correlating in-vitro data with protection in an animal model of HIB bacteremia and meningitis. Possible protective effects of antibodies to noncapsular antigens of HIB will be studied in an effort to determine if these might be useful as an alternative means of immunization against HIB dieseas. The genetics of the immune response to HIB infection and of susceptibility to HIB infection will be studied using inbred strains of rats.